Exploring the factors shaping microscopic morphological traits: insights from the chrysophycean genus Synura (Stramenopiles)

Synura represents a common freshwater protist genus known for producing morphologically diverse silica scales with species-specific secondary structures. In this study, we analysed 19 scale-bearing morphological traits across over 700 genetically verified records, spanning a broad environmental gradient in Europe. Focusing on Synura from section Petersenianae, we identified 29 species-level lineages, 13 of which had not been previously described. Interestingly, while species diversity increased northwards, morphological trait diversity exhibited the opposite trend, being higher in southern Europe. This suggests that abiotic factors play a significant role in shaping these traits, which are differently responsive to gradients than taxonomic diversity. We observed non-random distribution of scale morphological traits, influenced by abiotic factors such as temperature, precipitation and pH. Scale elongation appears to be an adaptation for living in oligotrophic waters with reduced sunlight availability, while the increasing distance between struts likely reflects an adaptation to low silica concentrations. Notably, specific morphological traits may provide more informative insights into environmental drivers than taxonomic units. The study sheds light on the intricate relationship between environmental conditions and the morphology of silica scales, emphasizing the importance of considering both taxonomic and morphological diversity in ecological research. Nanostructures of Synura silica scales represent unique morphological traits in protists.The distribution of microscopic traits on silica scales correlates with abiotic factors such as temperature, precipitation and pH.Specific morphological traits may provide more informative insights into environmental drivers than taxonomically based units. Nanostructures of Synura silica scales represent unique morphological traits in protists. The distribution of microscopic traits on silica scales correlates with abiotic factors such as temperature, precipitation and pH. Specific morphological traits may provide more informative insights into environmental drivers than taxonomically based units.